The present invention relates to a method for producing a fluoroaryl metal compound such as bis(pentafluorophenyl)dimethyltin or bis(pentafluorophenyl)dibutyltin, which is useful, for example, as a pharmaceutical and agricultural chemical intermediate, a polymerization catalyst, a polymerization co-catalyst, a catalyst for photopolymerization of silicone, and intermediates of these catalysts.
A fluoroaryl metal compound such as bis(pentafluorophenyl)dimethyltin or bis(pentafluorophenyl)dibutyltin is a useful compound, for example, as a pharmaceutical and agricultural chemical intermediate, a polymerization catalyst, a polymerization co-catalyst, a catalyst for photopolymerization of silicone, and intermediates of these catalysts.
For example, J. Chem. Soc., (1964) 4782 discloses a method for reacting pentafluorophenyl magnesium bromide (a Grignard reagent), obtained by reacting bromopentafluorobenzene with magnesium using diethyl ether as a solvent, with dimethyltin dibromide over two days at a reflux temperature, and for synthesizing bis(pentafluorophenyl)dimethyltin in a yield of 58 percent.
Besides, for example, Japanese Unexamined Patent Publication No. 2000-191666 (Tokukai 2000-191666, published on Jul. 11, 2000: corresponding U.S. Pat. No. 6,235,222) discloses a method for safely, efficiently, and industrially producing fluoroaryl magnesium halide having no impurities such as a coloring ingredient, through a reaction milder than a conventional method, by performing the Grignard exchange reaction of hydrocarbon magnesium halide such as magnesium methyl bromide and fluoroaryl halide such as bromopentafluorobenzene in a solvent including a chain ether solvent.
Further, for example, Organometallics., (1998) 5492 discloses a method for reacting pentafluorophenyllithium, obtained by reacting bromopentafluorobenzene with butyllithium at xe2x88x9278xc2x0 C. using diethyl ether as a solvent, with dimethyltin dichloride at xe2x88x9278xc2x0 C., and for synthesizing bis(pentafluorophenyl)dimethyltin in a yield of 95 percent.
However, in the production method described in J. Chem. Soc., (1964) 4782, since diethyl ether, which is a compound having a low boiling point, is used as the solvent, it is difficult to control the temperature of a reaction system, and special caution is required in handling diethyl ether as it is highly flammable. In addition, a diethyl ether solution of pentafluorophenyl magnesium bromide, obtained by reacting bromopentafluorobenzene with magnesium, is colored in black by impurities formed by a side reaction, etc. Therefore, the bis (pentafluorophenyl) dimethyltin obtained by reacting pentafluorophenyl magnesium bromide with dimethyltin dibromide is colored in black, and in order to purify the bis(pentafluorophenyl)dimethyltin, it is necessary to distill the reaction solution which contains the compound.
Further, in the foregoing production method, the reaction of pentafluorophenyl magnesium bromide and dimethyltin dibromide produces not only the bis(pentafluorophenyl)dimethyltin, which is an object, but also magnesium dibromide, which is magnesium halide, as a by-product. Since magnesium dibromide is soluble in a solvent such as diethyl ether, in order to purify the bis(pentafluorophenyl)dimethyltin, it is necessary to remove the magnesium dibromide from a solution. Besides, J. Chem. Soc., (1964) 4782 discloses a method for removing magnesium halide by treating a reaction solution containing the magnesium halide using an aqueous ammonium chloride solution. However, when the reaction solution is treated with the aqueous ammonium chloride solution, it becomes difficult to separate an organic layer and an aqueous layer. Therefore, it is hard to say that the production method described in J. Chem. Soc., (1964) 4782 is industrially advantageous. Incidentally, when a fluoroaryl metal compound which includes magnesium halide as an impurity is used, for example, as a polymerization catalyst, the activity of the catalyst is significantly decreased.
The problem that pentafluorophenyl magnesium bromide is colored by impurities formed by a side reaction, etc. described in J. Chem. Soc., (1964) 4782 can be solved by obtaining pentafluorophenyl magnesium halide having no impurities such as a coloring ingredient by the Grignard exchange reaction in the method for producing fluoroaryl magnesium halide disclosed in Japanese Unexamined Patent Publication No. 2000-191666 (Tokukai 2000-191666, published on Jul. 11, 2000: corresponding U.S. Pat. No. 6,235,222). However, Japanese Unexamined Patent Publication No. 2000-191666 does not have descriptions that tin is further reacted with fluoroaryl magnesium halide, and that fluoroaryl magnesium halide can be used as a raw material, as an intermediate of a specific fluoroaryl metal compound, etc.
On the other hand, in the production method described in Organometallics., (1998) 5492, the reaction system should be cooled down to xe2x88x9278xc2x0 C., which is difficult to carry out industrially.
Consequently, a method for producing and purifying a fluoroaryl metal compound easily and inexpensively has been desired.
It is therefore an object of the present invention to provide a method for producing and purifying a fluoroaryl metal compound which has no impurities and is less colored, easily and inexpensively.
To solve the foregoing problems, in the present invention, consideration has been given to various synthesis routes other than the foregoing conventional synthesis reactions, in order to synthesize pentafluorophenyl magnesium bromide, which is an intermediate, in the process for synthesizing bis(pentafluorophenyl)dialkyltin, which is a final object. As a result, we have reached a different synthesis route which has less side reaction and is less colored by produced impurities. Specifically, the different synthesis route is to carry out the Grignard exchange reaction, and we have invented a new synthesis route to obtain bis(pentafluorophenyl)dialkylthin, which is the final object, efficiently and with less coloring, by further reacting pentafluorophenyl magnesium bromide, which is the intermediate synthesized by the different synthesis route (the Grignard exchange reaction), with dialkyltin dichloride.
Since fluoroaryl magnesium halide, specifically, pentafluorophenyl magnesium bromide, which is the foregoing intermediate, has less side reaction in the synthesis route adopted in the present invention, the obtained pentafluorophenyl magnesium bromide is not colored. Therefore, it is possible to use the pentafluorophenyl magnesium bromide for the next process without purifying it. Besides, when the fluoroaryl magnesium halide is further reacted with an organic metal compound, even after a series of processes, specifically, even after consecutive processes, it is also possible to obtain a less colored fluoroaryl metal compound, which is the final object. Consequently, the synthesis route of the present invention is a very useful synthesis route which can simplify a series of processes. That is, in the production method of the present invention, it is possible to obtain the fluoroaryl metal compound, specifically, bis(pentafluorophenyl)dialkyltin, which is the final object, by further reacting the fluoroaryl magnesium halide, specifically, pentafluorophenyl magnesium bromide, which is the intermediate, with the organic metal compound in a series of processes, without purifying the fluoroaryl magnesium halide. More specific structure will be described below.
In order to solve the foregoing problems and to attain the foregoing object, a method for producing a fluoroaryl metal compound of the present invention, which is represented by General Formula (5): 
where each of R1, R2, R3, R4, and R5 independently represents one of a hydrogen atom, a fluorine atom, a hydrocarbon group, and an alkoxy group, provided that at least three of R1-R5 represent fluorine atoms, M represents a metal atom which belongs to the group IV, R6 represents a hydrocarbon group, and n represents one of 1 through 3, is characterized by including the steps of:
reacting hydrocarbon magnesium halide represented by General Formula (1):
R7MgXaxe2x80x83xe2x80x83(1)
xe2x80x83where R7 represents a hydrocarbon group, and Xa represents one of a chlorine atom, a bromine atom, and an iodine atom, with fluoroaryl halide represented by General Formula (2): 
xe2x80x83where each of R1, R2, R3, R4, and R5 independently represents one of a hydrogen atom, a fluorine atom, a hydrocarbon group, and an alkoxy group, provided that at least three of R1-R5 represent fluorine atoms, and Xc represents one of a bromine atom and an iodine atom, in a solvent including an ether solvent, so as to obtain fluoroaryl magnesium halide represented by General Formula (3): 
xe2x80x83where each of R1, R2, R3, R4, and R5 independently represents one of a hydrogen atom, a fluorine atom, a hydrocarbon group, and an alkoxy group, provided that at least three of R1-R5 represent fluorine atoms, and Xa represents one of a chlorine atom, a bromine atom, and an iodine atom; and
reacting the fluoroaryl magnesium halide with an organic metal compound represented by General Formula (4):
(R6)4xe2x88x92nM(Xb)nxe2x80x83xe2x80x83(4)
xe2x80x83where R6 represents a hydrocarbon group, n represents one of 1 through 3, M represents a metal atom which belongs to the group IV, and Xb represents a halogen atom.
A more specific embodiment of the method for producing the fluoroaryl metal compound of the present invention is further characterized in that the metal atom in the organic metal compound represented by General Formula (4) is tin.
A more specific embodiment of the method for producing the fluoroaryl metal compound of the present invention is characterized in that the fluoroaryl metal compound, which is the object compound, is bis(pentafluorophenyl)dialkyltin.
In the present invention, since the fluoroaryl magnesium halide is first synthesized by a specific synthesis route, that is, the fluoroaryl magnesium halide is prepared beforehand by carrying out the Grignard exchange reaction, the fluoroaryl magnesium halide less colored by a by-product can be obtained. Then, by using the less colored fluoroaryl magnesium halide as an intermediate material and further reacting it with an organic metal compound, specifically, an organic tin compound, a less colored fluoroaryl metal compound can be obtained as the final object. Besides, in order to separate the fluoroaryl metal compound, which is the object, and the magnesium halide, which is the by-product, after the reaction, it is a preferable embodiment of the production method of the present invention to carry out a purifying method (a) for precipitating the magnesium halide out of the reaction solution and filtering the precipitation, or a purifying method (b) for treating the reaction solution with an acid and easily removing impurities. The specific technique in the foregoing method (a) is a technique in which a hydrocarbon solvent such as hexane, a solvent which does not dissolve the magnesium halide, is added, precipitated as solid matter and filtered. In this manner, by carrying out a process to further purify the less colored fluoroaryl metal compound, which is the object obtained as a result of the Grignard exchange reaction carried out with the organic metal compound, as one process in a series of processes, the fluoroaryl metal compound which is less colored and has no impurities can be easily and inexpensively produced, and easily and inexpensively purified.